Electric current rectifying system



NOV. 26, 1935. H, MEYER-DELlUs 2,022,341

ELECTRC CURRENT RECTIFYING SYSTEM Filed Nov. 30, 1932 2 JWM/ww@ PatentedNov. 26, 1935 UNITED STATES PATENT OFFICE ELECTRIC CURRENT RECTIFYINGSYSTEM Heinrich Meyer-Delius, Heidelberg-Schlierbach,

Germany, assignor to Boveri & Cie., Baden,

Aktiengesellschaft Brown Switzerland, a joint-stock company ofSwitzerland 13 Claims.

This invention relates to improvements in electric current rectifyingsystems and more particularly to means for supplying a polyphase recktifier of the electron discharge type or a group of single phaserectifiers of such type with currents of a number of phases greater thanthe number of phases of the alternating current supply line.

Rectiiiers of the different types known in the art, and moreparticularly rectifiers of the gaseous or of the metallic vapor arcingtype, are most frequently supplied from three-phase alternating currentsupply lines with which they are connected by means of suitabletransformers. To obtain a suitable output voltage regulation in such asystem and to reduce the voltage ripple in the direct current outputcircuit thereof, the number of phases of Vthe transformer secondarywinding is usually increased from three to six by the connection ofintermediate points of the several winding portions thereof to form acommon neutral point, such connection being frequently obtained througha so-called interphase transformer. The number of transformer secondaryphases is also frequently increased to a number greater than six by theuse of additional transformer secondary windings or by suitableinterconnection of portions of the secondary winding which is thenprovided with taps to permit such interconnection. In particular, thesecondary winding of the transformer may consist of two six-phasesystems displaced with respect to each other by 30 electrical degreesand either directly interconnected or connected through an interphasetransformer to consti-` tute a lf2-phase systemvof connections. Suchconstruction of the secondary winding of the transformer presents thedisadvantage that, when the voltages of the three-phase supply line areunbalanced in magnitude or when such voltages present harmonics of thefundamental Wave, the secondary voltages of the transformer are nolonger of identical magnitudes with the result that the several anodesof the rectifier areunevenly loaded and that the direct current outputvoltage has a pronounced harmonic ripple. Another disadvantage of such asystem resides in the fact that the current drawn from the line by thesystem is not sinusoidal but presents a number of harmonics of which thefifth and the seventh are the largest and therefore the mostobjectionable.

It has been found by research that, when the secondary winding of thetransformer is formed by three symmetrical four-phase portions, the

current distribution between the anodes of the rectifier is not affectedby any unbalance in the primary voltages or by the presence of harmonicstherein. It has also been found that, in such a system, the harmonics inthe current drawn from the alternating current line are considerablyreduced and in particular that the fifth and seventh harmonics areentirely absent in such currents. The secondary winding portions maypreferably be interconnected by an interphase transformer to lengthenthe period of operation of each anode during each cycle of thealternating current supply line.

It is, accordingly, one object of the present invention to provide arectifying system insuring a uniform distribution of the current betweenthe several anodes of the rectifier.

Another object of the present inventon is to provide a rectifying systemin which the current distribution between anodes of the rectifier is notaffected by unbalances in the voltages of the supply line.

Another object of the invention is to provide a rectifying system inwhich the current distribution between anodes of the rectifier is notaffected by the presence of harmonics in the voltages of the supplyline.

Another object of the present invention is to provide a twelve phaserectifying system in which Y the currents drawn from a three-phasealternating current supply line do not have either fifth or seventhharmonics.

Another object of the present invention is to provide a twelve phaserectifying system cornprising a transformer having a three-phase primmary winding and a twelve phase secondary winding divided into threesymmetrical fourphase portions.

Another object of the present invention is to provide a twelve phaserectifying system comprising a transformer having a secondary windingsubdivided into three portions connected with the output line through aninterphase transformer.

Objects and advantages other than those above set forth will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. l diagrammatically illustrates one embodiment of the presentinvention consisting of a twelve phase rectifying system employing anelectric current rectifier of the metallic vapor arcing type, atransformer having a three-phase primary winding and a twelve phasesecondary winding subdivided into three symmetric fourphase portions,and an interphase transformer.

Fig. 2 is a diagram -of the no load voltages of the secondary windingsof the transformer utilized in the embodiment illustrated in Fig. 1.

Referring more particularly to the drawing by characters of reference,reference numeral 3 designates a three-phase alternating current supplyline supplyinCr current to the system. The rectifying system includes atransformer having a primary winding 4 herein illustrated as beingconnected in delta and receiving current from line 5. The transformersecondary winding comprises three symmetric four-phase portions 6, l and8 each comprising six winding portions connected as shown in the drawingand receiving, by induction from winding 4, voltages such as to obtainfour-phase alternating current voltages at the terminals thereof. Theterminals of windings 6, '5, and 0 are severally connected with theanodes 9 of rectifier II shown as being of the metallic vapor arcingtype having a cathode I2 of vaporizable material such as mercuryconnected with one of the conductors I3 of the direct current outputcircuit.

The neutral points of windings 6, 'I and 8 are severally connected withthe terminals of a threephase interphase transformer I5 having thewindings thereof arranged on a common core and presenting a neutralpoint connected with the second conductor I4 of the direct currentoutput circuit. Interphase transformer I5 is herein shown as beingconnected in zigzag because a star connection thereof would cause theproduction of direct magnetic flux in the core thereof as is well knownin the art.

It will be understood that rectifier II may be replaced by a pluralityof single phase rectiers of a similar type having their anodes severallyonnected with the terminals of windings 6, 1 .nd 8 and their cathodesconnected in common .rit'n conductor I3. Rectifier II may also bereplaced by a polyphase rectifier or by a plurality of single phaserectiers of the high vacuum type, thereby, however, introducing the Wellknown limitations of rectifiers of such character into the system.Rectifier I I may also be replaced by a plurality of single phaserectiers of the contact type such as the well known copper oxiderectifiers.

In operation, assuming that winding 4 is energized from line 3, eachsecondary Winding portion such as B presents, at the terminals thereof,symmetric four-phase voltages, the connections the windings being suchthat voltages in portion are displaced by 30 electrical degrees withrespect to the voltages in portion I and the voltages in portion l arealso displaced by 30 electrical degrees with respect to the voltages inportion 8, so that the terminal voltages of the entire secondary windingconstitute a twelve phase system of voltages. Due to the presence ofinterphase transformer' I5, each secondary winding portion such as 5operates as an independent source of supply for the associated anodes ofrectifier II. Assuming that an arc is ignited and is being maintained inrectifier II by the usual means (not shown), the anodes connected withthe terminals of winding 0 receive current sequentially during eachcycle of the supply line voltage, each anode therefore operating over aperiod of onequarter of a cycle. The terminal voltages of windingportions Ea, 8b, 8c and 6d are shown in Fig. at ida, leb, ISC and I6d,the corresponding carrying current during the peak portion of eachcurve. The voltages present between the neutral point of winding 6 andcathode I2 of rectifier II are then represented by curve 28 which liesbelow the peaks of curves IEa to IEd by the amount of the arc drop inrectier I I. Similarly the terminal voltages of winding portions I and 8are represented by curves Ila to Ild and I8a to I8d, and the voltagesbetween the neutral points of winding portions 'l and 8 and cathode I2are represented by curves 2T and 28 respectively.

Due to the action of the interphase transformer lo I5, the outputvoltage of the system applied to conductors I3 and I4 is equal to theaverage of the voltages represented by curves 26, 2'! and 28, thedifference between such average and the voltages shown by the curvesappearing at the terminals of interphase transformer I5. Suchtransformer, therefore, presents three-phase voltages of a frequencyhigher than that of the alternating current supply line, but which donot appear in either the supply line or in the output circuit. It willbe understood that curves 28, 2l and 28 are accurate only when thesystem is not carrying any load and will be somewhat distorted underload conditions due to the inductive drop of load currents in thetransformer windings. As will appear from Fig. 2, current is carriedsimultaneously at every instant by three anodes of rectifier II eachconnected with one of the secondary winding mrtions 6, I and 8, therebyinsuring a high degree of utilization of the rectifier 30 and of thetransformer.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent: 1. In a system ofthe character described, a

transformer comprising a secondary winding divided into three four phasesystems, and each phase of each system comprising a plurality of windingsections displaced 120 relative to each 45 other.

2. In a system of the character described, in combination, a transformercomprising a secondary winding divided into three portions of fourphases each and each phase of each portion comprising a plurality ofsections displaced 120D from each other and connected to form a neutralpoint, and an interphase transformer having Winding portions severallyconnected with said neutral points and having connections forming aneutral point.

3. In a system of the character described, a transformer comprising asecondary winding divided into three four phase portions formed of threemidtapped sections displaced 120 from 60 each other and connected ateach end thereof to two other sections displaced 120 one from anotherwhereby each said portion provider tour phases displaced 90 one fromanother, and an interphase transformer having winding portions severallyconnected with said znidtapped points `and having connections forming aneutral point.

4. In combination v-.dth a polyphase alternating current circuit, adirect current circuit, and electric current converting means comprisingcathode connected with said direct current circuit and a plurality ofanodes, of a transformer connected with said alternating ci eent circuitand having a winding divided into three similar symmetrically arrangedportions of four phases each and each said phase comprising a pluralityof sections displaced 120 from each other and severally connected withsaid anodes and having connections forming a neutral point connectionwith said direct current circuit, the number of phases and thesymmetrical arrangement of said portions being such as to preventdifferences in the magnitude of the alternating current circuit voltagesfrom affecting the current distribution in said portions of saidwinding.

5. In combination with a polyphase alternating current supply circuit, adirect current work circuit, and electric current rectifying meanscomprising a cathode connected with said work circuit and a plurality ofanodes, of a transformer having a primary winding connected with saidalternating current circuit and a secondary winding divided into threesimilar symmetrically arranged phase displaced portions, each comprisinga plurality of phase displaced sections severally connected with saidanodes and having connections forming a neutral point connection withsaid direct current circuit, the number of phases and the symmetricalarrangement of said portions being such as to prevent current offrequencies corresponding to the fth and seventh harmonic frequencies ofthe supply circuit from flowing thereto from said primary winding.

6. In combination with a polyphase alternating current circuit, a directcurrent circuit, and electric current converting means comprising acathode connected with said direct current circuit and a plurality ofanodes, of a transformer connected with said alternating current circuitand having a winding divided into three similar symmetrically arrangedphase displaced portions each comprising a plurality of phase displacedsections severally connected with said anodes and having connectionsforming a neutral point connection with said direct current circuit, thenumber of phase displaced sections and the symmetrical arrangement ofsaid portions being such as to prevent harmonic components of thevoltages of said alternating current circuit from affecting the currentdistribution in said portions of said Winding.

7. In combination with a polyphase alternating current circuit, a directcurrent circuit, and electric current converting means comprising acathode connected with said direct current circuit and a plurality ofanodes, of a transformer connected with said alternating current circuitand having a winding divided into three similar symmetrically arrangedphase displaced portions, each comprising a plurality of phase displacedsections severally connected with said anodes and having connectionsforming a neutral point connection with said direct current circuit, thenumber of phases and the symmetrical arrangement of said portions beingsuch as to prevent difierences in the magnitude and harmonic componentsof the alternating current circuit voltages from affecting the currentdistribution in said portions of said winding.

8. In combination with a polyphase alternating current supply circuit, adirect current work circuit, and electric current rectifying meanscomprising a cathode connected with said work circuit and a plurality ofanodes, of a transformer having a primary winding connected with saidcircuit and a secondary winding divided into three similar symmetricallyarranged phase displaced portions, each comprising four phase displacedsections severally connected with said anodes and having connectionsforming a neutral point connection with said work'circuit, the number ofphase displaced sections and the symmetrical arrangement of saidportions of said secondary winding being operable to prevent harmoniccomponents of the supply line voltages from affecting the currentdistribution in said portions and to prevent current of frequenciescorresponding to the fifth and seventh harmonic frequencies of thesupply circuit from flowing thereinto from said primary winding. l0

9. In combination with a polyphase alternating current circuit, a directcurrent circuit, and electric current converting means comprising acathode connected with said direct current circuit and a plurality ofanodes, of a transformer 15 connected with said alternating currentcircuit and having a winding divided into three similar symmetricallyarranged phase displaced portions, each comprising four phase displacedsections severally connected with said anodes and having 20 connectionsforming a neutral point, and an interphase transformer having a windingdivided into three portions severally connected with said neutral pointsand connected to form a neutral point connection with said directcurrent circuit, 25 the number of phase displaced sections and thesymmetrical arrangement of said portions being operable to preventharmonic components of the alternating current line voltages andunbalance thereof from affecting the current distribution 30 in saidportions of said Winding, and the said interphase transformer beingoperable to prolong the recurrent periods of flow of current throughsaid anodes by Way of said Winding sections.

1.0. In combination with a polyphase alternat- 35 ing current circuit, adirect current circuit, and an electric current converting meanscomprising a cathode connected With said direct current circuit and aplurality of anodes, of a transformer having a primary winding connectedwith said 40 alternating current circuit and having a winding dividedinto three similar symmetrically arranged phase displaced portionsformed of three phase midtapped sections connected at each end thereofto two other sections displaced 120 and 45 severally connected with saidanodes to form four phases displaced one from another, and an interphasetransformer having a winding divided into three .portions severallyconnected .with said midtapped points and having connec- 50 tionsforming a neutral point connection with said direct current circuit, thesaid interphase transformer being operable to prolong the recurrentperiods of flow of current through the respective anodes and saidconnected sections, 55 and the number of phases and symmetricalarrangement of said portions being operable to prevent harmoniccomponents and unbalance in magnitude of the voltages of the saidalternating current circuit from affecting the cur- 60 rent distributionin said portions of the first said transformer and to prevent current offrequencies corresponding to the fifth and seventh harmonic frequenciesof said alternating current circuit from fiowing thereinto from saidprimary wind- 65 ing.

11. In a system of the character described, a transformer comprising asecondary winding divided into three four phase portions, each formed ofthree midtapped sections displaced one 70 from another and connected ateach end thereof to two other sections displaced 120 one from another,whereby each said portion provides four phases displaced 90 one fromanother.

12. In a system of the character described, a 75 transformer comprisinga secondary winding divided into three foul` phase displaced portions toform a twelve phase system, the said phases severally comprising twophase displaced winding sections so proportioned that one sectionthereof contains substantially two and seventy-two one hundredths timesthe number of turns as the other section thereof.

13. in combination with a polyphase alternating` current supply circuit,a direct current work circuit, and electric current rectifying meanscomprising a cathode connected with said work circuit and a plurality ofanodes, of a transformer having a primary winding connected With saidsupply circuit and a secondary Winding divided into three similarsymmetrically arranged phase displaced portions each comprising aplurality of phase displaced sections severally connected with saidanodes and having connections forming a. neutral point connection withsaid direct current circuit, the number of phases and the symmetricalarrangement of said portions being such as to prevent the creation inthe voltage impressed on said work circuit from said rectifying means ofcomponents corresponding in frequency to the sixth harmonic frequency ofsaid supply circuit and odd multiples of such said harmonic frequency.

HEINRICH MEYER-DELIUS,

